Electromagnetic%20Waves

1
Electromagnetic Waves
2
Maxwells Equations

• Maxwells Equations
• Lorentz Force

3
Displacement Current

• Flowing current generates a magnetic field, but
  what about inside a capacitor where current
  doesnt flow?

B

• A changing electric field also generates a
  magnetic field.

E
4
Wave Propagation in 3-D

• Plane Waves - Crests of the 3 dimensional wave
  lie in a plane. Intensity remains constant.

5
Properties of EM Waves

• E B fields satisfy the same wave equation.
• EM waves travel at velocity,
• E B fields are perpendicular to each other and
  to the direction of travel.
• Magnitude of E B fields obey
• EM waves obey the superposition principle.

6
Polarization
Electric Wave

• Preferential orientation of the waves electric
  field vectors.

Magnetic Wave
7
EM Spectrum

• Radio waves
• Microwaves
• Infrared Light (IR)
• Visible Light
• Ultraviolet Light (UV)
• X-Rays
• Gamma Rays

Decreasing Wavelength
Increasing Frequency
Speed - 3.0 108 m/s
8
Energy in an EM Wave

• Poynting vector - Rate at which energy flows
  through a unit surface perpendicular to the flow.
  (Units, W/m2)
• Wave Intensity

Electric Wave
Magnetic Wave
9
Radiation Pressure

• Light has no mass however, it does have
  momentum.
• For complete absorption of light (inelastic
  collision), the pressure is
• For complete reflection of light (elastic
  collision), the pressure is

10
Doppler Shift

• For sound waves
• For light
• Light has no medium of propagation
• v is motion towards the observer

Star Spectra Sloan Digital Sky Survey
11
Evidences for IBB

• Hubble Constant
• Nucleosynthesis
• 73 H, 24 He, 3 other
• Microwave Background
• Large Scale Structure
• Evidence of Dark Matter

12
Young Creation Models

• How does distant light get to us?
• Light created in transit.
• Speed of light is slowing down.
• White hole cosmology
• Non-uniform properties of space

13
Big Bang Critique

• Quintessence
• Exotic Dark Matter
• Laws of Thermodynamics
• Inflation
• Exceed speed of light by 1024
• Not constrained enough
• ...supporters of Big Bang cosmology gain for
  themselves a large bag of free parameters that
  can subsequently be tuned as the occasion may
  require. (Burbidge, Hoyle, Narlikar)

Composition of the Universe 5 atoms, 26 dark
matter, 69 dark energy
14
Kepler Mission

• Description
• Launched March 2009
• View 145,000 stars near Cygnus
• Observe planet transits
• Stabilization failed May 2013
• Results as of Nov. 2013
• 2,300 planets (3601 unconfirmed)
• 10 earth sized in habitable zone
• Nearest maybe 12 light years away

15
Hubble Replacement - James Webb Space Telescope
2021